Idling speed control method and apparatus for an internal combustion engine

Abstract

An idling speed control method and apparatus in which the field current of an alternator is turned on and off to control the power generation rate of the alternator in accordance with the terminal voltage of a battery, and the air intake of an internal combustion engine is increased and decreased to keep the engine speed at a target speed during an idle operation of the engine such that the field current of the alternator is gradually increased toward a field current value corresponding to an electric load when the electric load is increased suddenly. A battery current consumption value is estimated from the detected state of the battery, a generated current value of the alternator is detected, the value of an electric load current to be outputted from the alternator is obtained in accordance with the sum of the estimated battery current consumption value and the generated current value of the alternator, and the air intake is increased when a set value is exceeded by the electric load current value.

What is claimed is: 
     
       1. An idling speed control method for an internal combustion engine, in which a field current of an alternator is turned on and off to control a power generation rate of the alternator in accordance with a terminal voltage of a battery, and an air intake of the internal combustion engine is increased or decreased to keep an engine speed at a target speed during an idle operation of the engine, such that, when an electric load suddenly increases during the idle operation of the engine, the field current of the alternator is gradually increased toward a field current value corresponding to the suddenly increased electric load, comprising: detecting the battery voltage;   estimating a battery current consumption value from a state of change in the detected battery voltage;   determining a generated current value of the alternator without directly detecting current generated by the alternator;   calculating a target value of an electric load current to be outputted from the alternator, based on the estimated battery current consumption value and the determined current value of the alternator; and   increasing the air intake based on the calculated target value of the electric load current,   wherein said air intake is increased when a first set value is exceeded by the calculated target value of the electric load, and an increment of said air intake is set based on a difference between the calculated target value and a second set value, and   wherein said intake air is increased only when such detected battery voltage decreases to an extent that charging of the battery is required due to the determined alternator current value.   
     
     
       2. The idling speed control method according to claim 1, wherein said second set value is set to be smaller than said first set value. 
     
     
       3. The method of claim 1, wherein said estimating step estimate the battery current consumption value from a difference between the detected battery voltage and a reference value. 
     
     
       4. An idling speed control apparatus for an internal combustion engine, which includes a battery, an electric device, an alternator adapted to be rotated by the engine to supply electric power to the electric device and charge the battery, and alternator control unit adapted to turn on and off a field current supplied to the alternator, thereby controlling a power generation rate of the alternator in accordance with a terminal voltage of the battery, such that when an electric load of the electric device suddenly increases, the field current of the alternator is gradually increased toward a field current value corresponding to the suddenly increased electric load of the electric device, and an air intake control valve provided in an intake passage of the engine, and in which the air intake of the engine is increased and decreased by opening and closing the air intake control valve, to keep an engine speed at a target speed during an idle operation of the engine, comprising: battery voltage detecting means for detecting the battery voltage;   estimating means for estimating a battery current consumption value from a state of change in the detected battery voltage;   current detecting means for determining a generated current value of the alternator without directly detecting current generated by the alternator;   load current value calculating means for calculating a target value of an electric load current to be outputted from the alternator based on the estimated battery current consumption value and the determined current value of the alternator; and   valve opening control means for increasing the opening of the air intake control valve based on the calculated target value of the electric load current,   wherein said air intake is increased when a first set value is exceeded by the calculated target value of the electric load, and an increment of said air intake is set based on a difference between the calculated target value and a second set value, and   wherein said intake air is increased only when such detected battery voltage decreases to an extent that charging of the battery is required due to the determined alternator current value.   
     
     
       5. The idling speed control apparatus according to claim 4, wherein said second set value is set to be smaller than said first set value. 
     
     
       6. The apparatus of claim 4, wherein said estimating means estimates the battery consumption value from a difference between the detected battery voltage and a reference value.